1. Field of the Invention
This invention relates to improvements in a throttle valve device of a V-type internal combustion engine, and more particularly to a throttle valve device including a mechanism for operating a throttle valve in relation to an acceleration operation and another mechanism for operating the throttle valve independently of the acceleration operation.
2. Description of the Prior Art
A throttle valve device has been proposed to be provided with a mechanism for operating a throttle valve in relation to an acceleration operation and another mechanism for operating the throttle valve independently of the acceleration operation, as disclosed in Japanese Patent Provisional Publication No. 3-50341. The throttle valve device includes a throttle shaft on which a throttle valve or plate is fixedly mounted to rotate around the axis of the shaft. One end section of the throttle shaft is provided with an acceleration drum to which an end of an acceleration wire is engaged. The other end section of the throttle shaft is provided with a gear mechanism. A step motor is provided on the opposite side of the gear mechanism with respect to throttle valve so that the rotational drive force of the step motor is transmitted through the gear mechanism to the throttle shaft.
With such an arrangement, the throttle valve is operated to open or close in relation to the acceleration operation through the acceleration drum, while it can be additionally operated to open or close independently of the acceleration operation, for example, by electronically controlling the opening degree of the throttle valve to control a slip ratio of a road wheel at a suitable value thus accomplishing a so-called traction control.
However, drawbacks have been encountered in the above conventional arrangement particularly in a case that the throttle valve device is installed to a V-type engine such that a throttle chamber is located to extend along the rows of engine cylinders and between banks in plan. That is, in the conventional throttle valve device, the step motor projects far from the end section of the throttle shaft, and therefore the conventional throttle valve device become unavoidably wider in the axial direction of the throttle shaft. As a result, the throttle valve device interferes with the cylinder heads, rocker covers or/and the like, so that the location of the throttle chamber is required to be shifted.
Here, the shift of the throttle chamber to an upward position is restricted by an engine hood. In general, the height of the engine hood decreases in a direction toward the front of the vehicle, and therefore the allowable height of the throttle chamber seems to increase by locating the throttle chamber at the rear side of the engine compartment and between the banks. However, in a case that the width of the throttle valve device increases owing to the above-identified disposition manner of the motor, shifting the throttle chamber to a much higher position is required thereby to further raise the height of the engine hood as compared with the case of a throttle valve device providing no mechanism for operating the throttle valve by a motor.
Additionally, it may be proposed to shift the position of the throttle chamber toward the ends of the banks so as to locate at least the motor out of the space defined between the banks in order to prevent the throttle valve device from interference with the cylinder heads, rocker covers and/or the like. However, in this case, the length of the engine in the direction of the cylinder rows will be unavoidably enlarged thereby requiring an enlargement of the engine compartment.